This is a national stage of PCT/EP99/03376 filed May 17, 1998 and based upon German national applications 198 22 304.8 of May 18, 1998 and 198 34 881.9 of Aug. 1, 1998 under the International Convention
This invention relates to a fluidized-bed firing system with generation of steam for the combustion of solid fuels and for generating steam.
Such systems, which are advantageous for smaller power outputs, are known for instance from EP-B-0365723, EP-A-0416238 as well as DE-A-3107356 and DE-A-4135582. In the known plants, only a single fluidized-bed combustion chamber is associated with a heat-exchange chamber. For large plants, which generate a large amount of steam that is used in power plants with more than 250 MW (electrical) capacity, the known systems are not advantageous.
It is the object of the invention to provide a fluidized-bed firing system in a compact design such that it can be built as a block requiring little space.
In accordance with the invention this achieved in
a) that in a heat-exchange chamber with an inner (internal) height of at least 10 m, there are disposed heat-exchange elements through which flows a cooling fluid, and the heat-exchange chamber has four vertical outer walls which enclose a space approximately rectangular in horizontal cross-section.
b) that outward of a first outer wall of the heat-exchange chamber a first fluidized-bed combustion chamber is disposed, and outwardly of a second outer wall of the heat-exchange chamber opposite the first outer wall a second fluidized-bed combustion chamber is disposed, where the inner height of the fluidized-bed combustion chamber is 10 to 60 m and preferably at least 20 m, and each fluidized-bed combustion chamber has lines for supplying fuel and combustion air, and
c) that with the upper portion of each fluidized-bed combustion chamber at least one separator is connected for separating solids from a gas stream, which separator has at least one gas-carrying discharge line connected with the heat-exchange chamber.
In one embodiment of the invention, each fluidized-bed combustion chamber is associated with at least one fluidized-bed cooler which is disposed below a separator and is connected therewith by a solids-carrying line. Each fluidized-bed cooler is connected with the associated fluidized-bed combustion chamber through at least one line carrying solids and/or gas.
The plant in accordance with the invention can be designed and build as a compact block. At the same time it is possible easily to arrange one or more blocks one beside the other in a space-saving way with or without physical separation. Inside each block, the central arrangement of the heat-exchange chamber provides for an inexpensive construction due to short lines for the combustion air delivered to the fluidized-bed combustion chambers, which combustion air is preheated in the heat-exchange chamber or in other suitable means. Each fluidized-bed combustion chamber may be connected with the associated fluidized-bed cooler to form a static unit, where the fluidized-bed cooler can be designed as a mounted construction or can be suspended from the fluidized-bed combustion chamber. A particularly space-saving design of the firing system is obtained in that the distance between the first fluidized-bed combustion chamber and the first outer wall as well as the distance between the second fluidized-bed combustion chamber and the second outer wall of the heat exchanger chamber is 0 to 2 m.
The firing system in accordance with the invention is designed for big plants. In general, the cross-sectional area of each of the two fluidized-bed combustion chambers, measured in a horizontal plane and at half height of the interior of the chamber, will be 50 to 300 m2 and preferably at least 70 m2. Usually, the interiors of the first and second fluidized bed combustion chambers will be approximately rectangular in horizontal cross-section. For very big plants, two or more heat-exchange chambers and at least three fluidized-bed combustion chambers can be arranged side-by-side alternatingly.